The present invention relates to a front and rear wheel drive motorcycle adapted to be driven on a sandy ground or a road having a soft road surface condition and more particularly to front and rear wheel drive motorcycle provided with non-stage speed change belt mechanism.
Generally, a motorcycle is provided with an engine to which a multi-stage gear transmission mechanism is connected through a manual clutch and the engine is operatively connected to a rear wheel through a chain to drive the rear wheel. Namely, the motorcycle of this type is run by driving the rear wheel and is steered by the front wheel. The speed change gears of the multi-stage gear transmission mechanism are selectively switched in accordance with a running speed of the motorcycle. The output of a power transmission shaft is branched through a differential clutch to drive the front wheel as disclosed in the Japanese Patent Laid-open Publication No. 58-206477, for example. The Japanese Laid-open Publication No. 61-181789, for example, discloses a three-wheeled vehicle in which the differential mechanism is eliminated between the front and rear wheels to drive onlY the front wheel.
For the motorcycle in which only the rear wheel is driven by the engine, it may become impossible to be smoothly driven when the rear wheel loses traction and slips, particularly when riding on sandy ground or soft road. On the other hand, for a motorcycle in which front and rear wheels are driven, it is necessary for a differential clutch or a differential mechanism to compensate for a rotation difference between the front and rear wheels due to the steering operation of the front wheel. In addition, for the differential mechanism, it is necessary to provide a slip preventing mechanism capable of driving the motorcycle by transmitting the driving force to one wheel when the other slips wheel. This complicates the structure of the mechanisms and, hence, the motorcycle itself, resulting in an increase of the manufacturing cost. Moreover, when riding on sandy ground or soft road, the wheels of the motorcycle receive large friction resistance from the road. Accordingly, the running speed of the motorcycle is extremely reduced during the changing operation of a speed change gear mechanism in the multi-stage gear transmission mechanism, thus being inconvenient for the smooth driving of the motorcycle.